Have you contacted Sender Support at Microsoft? They're very responsive and if your mail activity is legit they'll certainly help you solve the issue. Also make

Have you contacted Sender Support at Microsoft? They're very responsive and if your mail activity is legit they'll certainly help you solve the issue. Also make sure you set up the SNDS dashboard so you can view your IP reputation: https://sendersupport.olc.protection.outlook.com/snds/index.aspx https://sendersupport.olc.protection.outlook.com/snds/index.... In my experience the difference in outcomes that people have with self-hosting mail are largely down to, from most important to least, (1) the nature of the mail they are sending, (2) their choice of hosting provider, and (3) the correctness of their mail server setup. It sounds like you've got (3) sorted, so maybe (1) or (2) are relevant here.